Incursions - How HIGH does a runway's airspace extend?
I have done some looking and I cannot seem to find any regs about the altitude limit of a runway's airspace in terms of considering incursions. If an airport has crossing runways and an aircraft is lined up on one, where another is taking off on the other, the second aircraft gets airborne and 'crosses' the lined up aircraft's runway at 100 feet, then this might be an incursion, but if another aircraft overflys the field above circuit height, then this is obviously not an incursion.
But what if the crossing aircraft was already at 500 feet AGL when he crossed the other runway. Would that be an incursion? What if the overflying aircraft was at 500 feet, AGL. Would that be.
I imagine that the runway's 'airspace' would extend up to circuit height. Is that an accurate estimation? I also imagine it might differ between controlled and non-controlled airports.
What are the regulations on this?